Ohio State football coach Jim Tressel said the hit that knocked Buckeyes receiver Dan Herron out of Saturday's game at the University of Wisconsin with a concussion was a helmet-to-helmet collision and warranted a penalty, the Columbus Dispatch reported.

Tressel has asked the Big Ten Conference to review the hit, which was delivered by Badgers safety Jay Valai, because no flag was thrown on the play.

The league emphasized this preseason that it would more rigorously enforce helmet-to-helmet contact, which was outlawed several years ago and carries a 15-yard penalty.

Notably, the instructional video advising officials of the emphasis featured a play last year in which Wisconsin receiver Kyle Jefferson was the recipient of a helmet-to-helmet collision delivered by Michigan State's Nehemiah Warrick. No penalty was called on that play.

Herron did not see Valai coming as he ran across the field while trying to get the attention of scrambling Ohio State quarterback Terrelle Pryor. Trainers immediately rushed onto the field, indicating the severity of the injury.

While noting that he was "not pointing fingers" at Valai for willfully intending to break the rules or injure Herron, Tressel said that after reviewing film, the hit "certainly" was a collision between "head gear and chin."

Valai actually knocked two Buckeyes receivers out of the game with concussions. Receiver Dane Sanzenbacher was injured on a third-quarter play in which Valai hit him in the open field, forcing a fumble after a 23-yard gain.

Tressel said that neither Herron nor Sanzenbacher will play this week against Purdue.

Ironically, UW coach Bret Bielema asked Big Ten officials to review a play after the 2007 meeting between the Badgers and Buckeyes in which cornerback Allen Langford sustained a season-ending knee injury.

Ohio State wide receiver Brian Hartline dove at the knees of Langford, who wasn't looking, during a running play late in the first quarter of the Buckeyes' 38-17 victory at Ohio Stadium. Langford tore the ACL in his knee and missed the final two games of the season.

Bielema and his staff felt the block was illegal because Langford was defenseless on the play, but Big Ten officials ruled it was a legal block.